Calculate system idle time without hooks

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Introduction

This article described code for calculating for how long a system has been idle. This is useful to do background work etc. There might be other similar articles on the web and/or CodepPoject; if you find a better way, please do let me know. The attached sample is a simple WinForms application to demonstrate the code.

Background

I was browsing the web and encountered a couple of articles on how to calculate idle time, but they were doing it using system wide hooks. We don't want to install hooks, do we? Especially for a simple task like calculating system idle time. So, the result is this article.

Using the code

The code is very simple, just a couple of Windows API function calls.

Dim idleStruct As LASTINPUTINFO
idleStruct.cbSize = Marshal.SizeOf(idleStruct)
'check if we are able to calculate time.
If GetLastInputInfo(idleStruct) Then
    Dim sysIdleTime As Integer = GetTickCount() - idleStruct.dwTime
    Dim totalTime As New TimeSpan(sysIdleTime * 10000)
End If

All we need to do is create an object of the LASTINPUTINFO structure. Before passing it as a parameter, set its size using the Marshal.SizeOf method. The function GetLastInputInfo is used to populate the dwTime property of the LASTINPUTINFO structure. If the function is successful, it returns true; otherwise false. Once the dwTime is populated, we call another function GetTickCount; what this does is it calculates the time since the Windows session was started. And, the API declarations are as follows:

''' <summary>
''' Structure for last input infomation.
''' </summary>
''' <remarks>More info about
''' it http://msdn.microsoft.com/en-us/library/ms646272(VS.85).aspx
''' </remarks>
<StructLayout(LayoutKind.Sequential)> _
       Public Structure LASTINPUTINFO
    Public cbSize As Integer
    Public dwTime As Integer
End Structure


''' <summary>
''' Function to get the last input value.
''' </summary>
''' <param name="lii"></param>
''' <returns>Returns true on sucess and false on failure.</returns>
''' <remarks>More info about it http://msdn.microsoft.com/
'''      en-us/library/ms646302(VS.85).aspx</remarks>
Public Declare Function GetLastInputInfo Lib "User32.dll" _
              (ByRef lii As LASTINPUTINFO) As Boolean


''' <summary>
''' Get the time since windows started.
''' </summary>
''' <returns></returns>
''' <remarks>http://msdn.microsoft.com/en-us/library/ms724408(VS.85).aspx</remarks>
Public Declare Function GetTickCount Lib "kernel32" _
               Alias "GetTickCount" () As Integer

Conclusion

I hope this article helps my fellow developers. If you like this article, please do vote for it. And, if you find a bug or improvement, do let me know.